IE54698B1 - Grab - Google Patents

Abstract

A grab comprising two grab buckets (2,3) pivoted together by means of plate-like carrier arms (15,16,22,23) mounted on a pivotal shaft (8). The carrier arms (15,16,22,23) extend from the bottom of a bucket to beyond the pivotal shaft (8) and are substantially parallel to each other. The carrier arms (15,16) of one bucket (2) are located on opposite sides of a median plane perpendicular to the pivotal shaft. The two carrier arms (15,16) are interconnected at least at their ends (19) and provided with guide pulleys and "close" pulleys (11,12) for guiding the closing ropes (6). The ends (27,28) of the carrier arms (22,23) of the other bucket (3) are made of double-walled construction by means of stiffening plates (25,26) connected to them in spaced relationship thereto. The carrier arms are arranged to pass by each other, so that the grab can be fully opened (FIG. 2b). Closing ropes (6) are secured to the ends of the carrier arms (22,23) of the other bucket (3).

Description

This invention relates to a grab.

A prior grab of the type to which the present invention relates is described in Netherlands Patent Application No. 6711276. This prior grab comprises two buckets pivoted together by means of pairs of plate-like carrier arms, said carrier arms extending beyond the pivotal axis and, in the open position of the grab, being located in side-by-side relationship, each carrier arm of at least one pair of carrier arms associated with one bucket being of substantially planar shape, which carrier arms of that pair are connected together at their ends, which end is provided with guide pulleys and close pulleys for guiding and closing ropes, each bucket being connected to a yoke by means of one or more ropes.

This prior grab has a large number of excellent service characteristics, achieved mainly owing to the carrier arms being offset inwardly relatively to the side walls of the grab buckets. A structural problem in this connection is that the ends of the two pairs of carrier arms are interconnected, between which ends parts of the pulley box are arranged with guide pulleys and close pulleys, as well as push pulleys for the closing ropes. A push pulley in this connection means one which causes the closing rope, in the open position of the grab, to pass at some distance over the pivot point in order that the grab may be closed with less effort, i.e., with a smaller tensile force in the rope. This construction renders it necessary that at least one pair of carriers arms, the portions located beyond the pivotal axis should be located inwardly of the carrier arms of the other grab bucket for the simple reason that, otherwise, the ends of the carrier arms could not pass each other. One pair of carrier arms, therefore, is divided, the portion intermediate the grab bucket and the pivotal axis being located outwardly of the carrier arms of the other grab bucket, while the portion beyond the pivotal axis is located inwardly of the carrier plates of the other grab bucket. This leads necessarily to a rather expensive and heavy pivot construction, 2. 5469S because the torque brought about in the carrier arms by the closing forces is mainly transferred by way of this pivot by torsion.

It is an object of the present invention to provide a grab of the type described above, which is structurally simpler and lighter in weight. For this purpose, the grab according to the invention is characterized in that each carrier arm of the other bucket is also substantially of planar shape throughout its length, the portion of this carrier arm located beyond the pivotal shaft being provided with a stiffening plate spaced from that carrier arm portion, the end of said stiffening plate being connected to the end of this carrier arm to form a tine in which the end of a closing rope is secured.

As, in a grab thus formed, the ends of the tines are not interconnected, the carrier arms located on the outside are fully free to move along the outside of the inner carrier arms, so that the grab can be fully opened. During operation, and as a result of the closing force brought about by the closing ropes, the carrier arms are mainly subjected to bending loads, so that the main pivots can be made considerably simpler and in addition are easier to assembly and dissemble, while at the same time a considerable saving in weight is obtained. This saving in weight is even greater as the pulley box is accommodated in one bucket only, and has fewer pulleys. The additional result is that the reeving of the closing ropes is simpler and the reeved ropes are subjected to fewer bends.

Preferably, the stiffening plate extends from the tine tip in the direction of the sidewall of the associated bucket, and is connected therewith.

The end of each closing rope is fixed in a thimble holder which by means of a pin is pivotally connected to the end of a tine.

These tines offer the further advantage that their ends can be arranged more remote from the pivot of the grab, so that a larger closing force can be realised, both in the closed position of the grab and at the beginning of the closing movement in the open position of the grab.

In order that the buckets may have sufficient rigidity in the transverse direction, preferably each grab bucket is provided with 3. transverse stiffening tubes parallel to the pivotal shaft, one stiffening tube being secured in one bucket between the carrier arms, and the other being secured in the other bucket between the carrier arms and the sidewalls of that bucket.

The guide pulleys of the pulley box of the grab are preferably arranged on the inside of the carrier arms nearest the longitudinal axis of the grab, while the "close pulleys are located outwardly of the carrier arms.

In another embodiment, both the guide pulleys and the close pulleys are arranged inwardly of the carrier arms nearest the longitudinal axis of the grab, which carrier arms are slightly bent outwardly at the location of the close pulleys. The slightly offset construction of the carrier arms makes the construction more expensive, it is true, but this is, at least partly, compensated by the considerably more favourable reeving pattern of the ropes in this embodiment.

If the grab according to the invention takes the form of a transverse grab, which means that the opening direction of the grab is located substantially in the plane containing the hoist and closing ropes of the crane from which the grab is suspended, the buckets are made to exhibit rotary symmetry. In this construction each grab bucket is provided with two parallel, planar carrier arms, one of which carries guide pulleys and "close pulleys, and the other, together with a stiffening plate arranged in spaced relationship thereto, forms a tine, at the end of which a closing rope of the other bucket is secured, and, in the mounted condition, the carrier arms with the guide pulleys and close pulleys of one bucket is located between the tine and the carrier arm with the guide pulleys and close pulleys on the other grab bucket.

Some embodiments of the grab according to the invention will now be described in more detail, by way of example, with reference to the accompanying drawings. In said drawings: 4.

Figure 1 shows a grab according to the invention in the closed condition; Figures 2a, 2b show a plan view and a front-elevational view, respectively, of the grab shown in Figure 1 in the open condition; Figures 3a, 3b show views similar to Figures 2a, 2b, of a slightly modified embodiment; Figures 4a, 4b show a plan view of a diagrammatic front-elevational view, respectively, of a grab in an embodiment exhibiting rotary symmetry.

The grab as shown in Figures 1, 2a and 2b comprises grab buckets 2, 3 connected by means of suspension ropes or chains 4 to a yoke 5. This yoke 5 is connected by means of hoist ropes 7 to the crane. The closing ropes 6 extend from the crane top through yoke 5 to the pulley box 10, which forms part of bucket 2. The pulley box houses guide pulleys 12 and close pulleys 11. The ends of closing ropes 6 are connected to the free ends of fork tines 9. Grab buckets 2, 3 are pivotable about a pivot shaft 8.

In Figure 2a, the shape and configuration of the carrier arms or shear plates is illustrated. The left bucket 2 is provided with two shear plates or carrier arms 15, 16 connected together by a stiffening tube 17, to which an eye 18 is secured for connecting a suspension rope 4 thereto. Shear plates 15,16 extend from the bottom of bucket 2 to beyond the pivot shaft 8. Shear arms 15,16 are interconnected at the end by a protection plate 19 which prevents the closing ropes from contacting the bulk material being handled. The space formed by the two shear plates 15, 16 and protection plate 19 houses two guide pulleys 12. Two close pulleys 11 are located outwardly of shear plates 15, 16 and are protected by outer plate elements extending from the shear plates to the protection plate 19. Sidewalls 20 of bucket 2 consist of Z-shaped bent plates, connected at one end to the pivot shaft 8.

The right-hand bucket 3, as shown In Figure 2a, is provided with carrier arms or shear plates 22, 23, which extend from the bottom of bucket to beyond the pivot shaft. Shear plates 22, 23 are located outwardly of shear arms 15,16 of grab bucket 2, and can fully pass by the latter. Shear plate 23 together with stiffening plate 25 forms one of the fork tines 9 . g y a with plates 23 and 25 being interconnected at the end 27. Stiffening plate 25 extends from tine tip 27 in the direction of pivot shaft 8 and subsequently merges into side walT 21 of grab bucket 3. Similarly, shear plate 22 and stiffening plate 26 together form the other fork tine 9, with plates 22, 26 being interconnected at their ends 28. At the position of the pivotal shaft, stiffening plate 26 merges into the sidewall 21 of grab bucket 3. Bucket 3 is stiffened in the transverse direction by means of tube members 24 arranged between shear plates 23, 22 respectively and sidewalls 21 of bucket 3. Mounted on these stiffening tubes 24 are eyes 18 for securing suspension ropes 4 thereto. The location of the stiffening tubes 17 and 24 provides the possibility for the grab to be suspended from three rather than the usual four ropes, the effect of which is a better static weight distribution over ropes 4.

Each closing rope 6 passes from the yoke (Figure 1) around a guide pulley 12, close pulley 11 and thence to one of the tine tips 27, 28.

The ends of the closing ropes 6 are fixed in thimble holders 29, mounted on swivel bearings and pivoted by means of pins 30 to tine tips 27, 28.

Figure 2b shows that closing ropes 6 are located well above the axis of pivotal shaft 8, the effect of which is a favourable closing characteristic of the grab. The closing characteristic of the grab is further favourably affected by the fact that all shear plates or carrier arms can extend beyond stiffening rods 17, 24 of buckets 2, 3 so that longer lever arms can be selected than in the case of shear grab described in Netherlands Patent Application 6711272, in which the shear arms must necessarily terminate in front of the transverse stiffening rods mounted 1n the grab buckets.

By virtue of the savings in weight that can be obtained with the grab shown in Figures 1 and 2, owing to various close and push pulleys being dispensed with and owing to the lighter construction of the fork tines and the pivots, this grab makes it possible to use the lifting capacity of the crane with greater efficiency. With a grab of conventional construction, the ratio between the weight of the contents and the overall weight was 27.5 divided by 50, so that the efficiency is 0.55. With the fork shear grab according to the present invention, the weight of the contents could be increased from 27.5 to 30 tons, so that the efficiency is 30 divided 6. 4 6 9 Β by 50 to 60S. The transfer capacity, too, is increased by a factor 30 divided by 27.5 is 1.09, or 9S.

The fork shear grab shown in Figures 3a, 3b corresponds to that of Figures 2a, 2b with the only difference being that, in the grab of Figure 3a, the shear arms 15, 16 are bent outwardly approximately halfway the pulley box, as a result of which the close pulleys 11 can be arranged inwardly of shear arms 15, 16. This means that at the underside of guide pulleys 12, the control of closing ropes 6 need not be passed through shear arms 15, 16 to close pulleys 11 but can remain fully within the space enclosed by shear arms 15, 16. This makes the reeving of the ropes more favourable, although this goes at the expense of a somewhat more expensive construction, because the shear plates 15, 16 have to be bent outwardly.

Figures 4a, 4b show a particular embodiment of the fork shear grab according to the invention, namely in case it is desired for the fork shear grab to be constructed as a transverse grab. In the shear grab of Figures 1 to 3, the opening direction of the grab is in a plane perpendicular to the plane containing the tube closing ropes 6, whereas in a transverse grab the opening direction must coincide with the plane containing the two closing ropes. A transverse grab must of course exhibit rotary symmetry, and this can be achieved by the variant of the grab of Figures 1 to 3 as shown in Figure 4. The particular feature of this transverse grab relative to the embodiments described hereinbefore, is that each grab bucket is provided with one fork tine and a continuous shear arm or carrier plate extending parallel thereto, whereas, in the embodiments described hereinbefore, one of the grab buckets was in each case provided with two fork tines.

The grab bucket 2 shown in Figure 4 is provided with a shear plate 32 extending from the bottom of bucket 2 longitudinally of the grab, and terminating in a fork tine 27. Mounted in spaced relationship to this shear plate 32 is a stiffening plate 31, extending from the tip of the tine in the direction of the pivot shaft 8, and merging into the sidewall 20 of bucket 2. Extending parallel to shear plate 32 is shear plate 33, also from the bottom of bucket 2. Shear plate 33 is of double-walled construction approximately from hinge shaft 8 onwards, by means of a plate 34 extending parallel to shear arm 33. Interposed between plates 33, 34 is 7. 54G98 "close pulley IT, while guide pulley 12' is mounted inwardly of shear plate 33, which pulley 12' is of course journalled in plates 33, 34.

Closing rope 6' passes round pulleys 12' and 11' and is next secured in a thimble holder connected to the fork tine of the other bucket 3, while the 1 closing rope 6, which is connected to the fork tine 27 of bucket 2, passes round guide and close pulleys 11, 12 associated with bucket 3.

Grab bucket 3 is entirely identical to grab bucket 2 and is likewise provided with a fork tine consisting of shear plate 32' and stiffening plate 3Γ, while a shear plate 33 is provided parallel to shear plate 32', which plate 33' is of double-walled construction at the end by means of a plate 34'. Provided between plates 33' and 34' is close pulley 11, while guide pulley 12 is journalled inwardly of shear plate 33'.

During the assembly of the two identical grab buckets 2, 3, one of the buckets is rotated through 180°, so that the shear plates 33' and 15 plate 34' connected to it come to lie between shear plates 32 and 33 of bucket 2. Owing to this construction and manner of assembly, the fork shear grab is fully balanced, i.e., the left-hand bucket is as heavy as the right-hand bucket, and there is no danger for the grab to start rotating about its axis perpendicular to the closing ropes 6, 6', and located approximately at the level of yoke 5.

Claims (9)

1. A grab comprising two buckets pivoted together on a pivotal shaft by means of pairs of plate-like carrier arms, said carrier arms extending from the buckets to beyond the pivotal axis of said shaft and, in the open position of the grab, being located side by side, each carrier arm of at least one pair of carrier arms associated with one bucket being of substantially planar shape, the carrier arms of said one pair being connected together at one end, which end is provided with guide pulleys and close pulleys for guiding the closing ropes, each bucket being connected to a yoke by means of one or more ropes, wherein each carrier arm of the other bucket is also substantially of planar shape throughout its length, the portions of these carrier arms located beyond the pivotal shaft being each provided with a stiffening plate spaced from said carrier arm portion, one end of said stiffening plate being connected to the end of the associated carrier arm to form a tine to which the end of a closing rope is secured.

2. A grab according to claim 1, wherein each stiffening plate extends from its connection with the associated tine in the direction of the sidewall of the associated bucket and is connected therewith.

3. A grab according to claim 1 or 2, wherein the end of each closing rope is fixed in a thimble holder which by means of a pin is pivotally connected to the end of the associated tine.

4. A grab according to any one of claims 1 to 3, wherein each grab bucket is provided with a transverse stiffening tube extending parallel to the pivotal shaft, one stiffening tube being secured in said one bucket between the carrier arms and the other stiffening tube being secured in the other bucket between the carrier arms and the sidewalls of that bucket.

5. A grab according to claim 4, which is connected to the yoke by means of three suspension ropes or chains, the lower ends of the ropes being secured to eyes provided on the transverse-stiffening tubes.

6. A grab according to any one of claims 1 to 5, wherein the guide pulleys are arranged on the inside of the carrier arms nearest the 9. longitudinal axis of the grab, and the “close pulleys are located outwardly of said carrier arms.

7. A grab according to any one of claims 1 to 5, wherein both the guide pulleys and the “close pulleys are arranged inwardly of the carrier arms 5 nearest the longitudinal axis of the grab, which carrier arms are slightly bent outwardly at the location of the close pulleys.

8. A grab having two grab buckets pivoted together by means of plate-like carrier arms, said carrier arms extending from the buckets to beyond the pivotal axis of said buckets and, in the open position of the 10 grab, being located side by side, wherein the grab buckets exhibit rotary synmetry, with each grab bucket being provided with two parallel, planar carrier arms, one of which carries guide pulleys and close pulleys and the other, together with a stiffening plate arranged in spaced relationship thereto, forms a tine, at the free end of which a closing rope of the other 15 bucket is secured, and, in the mounted condition, the carrier arms with the guide pulleys and close pulleys of one bucket is located between the tine and the carrier arms with the guide pulleys and close pulleys of the other grab bucket.

9. A grab, substantially as hereinbefore described with reference to and 20 as shown in Figures 1 and 2, Figure 3 or Figure 4, of the accompanying drawings.